1. Field of the Invention
The present invention relates to photographic lenses and photographing apparatus and, more particularly, to a photographic lens capable of focusing on an object in a wide range from infinity to as short distances with life-size magnification and a photographing apparatus having the photographic lens.
2. Description of Related Art
For a camera for photography, such as video camera or the still video camera, there has been developed a photographic lens that aims mainly at photographing close objects, or what is called the "macro" or "micro" lens (hereinafter generally referred to as the "macro" lens).
The macro lens is so designed that high optical performance is obtained when photographing an object especially at a closer distance than with other types of photographic lenses, such as the standard lens and telephoto lens in a normal image distance setting. Again, the macro lens is, in many cases, used even when shooting not only a close object but also an object in a wide range of distances from infinity to the minimum.
In general, with the macro lens, if it is intended to extend the focusing range toward shorter object distances (or the range of magnifications toward larger image sizes), aberrations vary with focusing to an even wider extent, increasing greatly particularly in closeup photography or at high reproduction ratios, and, therefore, become difficult to correct well in this region. So, as can be seen in Japanese Laid-Open Patent Application No. Sho 63-179308, a focusing method is proposed which uses at least two lens units arranged to axially move independently of each other, or utilizes the so-called "floating" technique. The of aberrations variation with focusing is thus minimized.
In the meantime, in Japanese Patent No. 2,556,986 and Japanese Laid-Open Patent Application No. Hei 4-110811, there has been proposed a photographic lens comprising, in order from an object side to an image side, a positive lens unit, a negative lens unit, a positive lens unit and a negative lens unit, wherein during focusing to closer object distances, the first and fourth lens units remain stationary relative to the image plane, the second lens unit moves toward the image side and the third lens unit moves toward the object side.
Also, in Japanese Laid-Open Patent Application No. Hei 8-76012, for the photographic lens comprising, in order from an object side to an image side, a positive lens unit, a negative lens unit, a positive lens unit and a negative lens unit, another method is proposed that, during focusing to closer object distances, the first lens unit remains stationary relative to the image plane and the second, third and fourth lens units move.
However, most of the macro lenses including that disclosed in Japanese Laid-Open Patent Application No. Sho 63-179308 employ the method of bodily moving the whole lens system forward. If a lens unit of a large size is selected to use in focusing, the driving torque of an electrically-operated control means such as a motor has to increase. In the auto-focus camera that moves the focusing lens unit by the electric motor, therefore, high-speed focusing becomes difficult to carry out.
The arrangements disclosed in the above Japanese Patent No. 2,556,986 and Japanese Laid-Open Patent Application No. Hei 4-110811, because of moving the second and third lens units of lighter weight than that of the first lens unit, are advantageous for automatic focusing. However, to assure maintenance of good stability of image quality over the entire extended focusing range from the setting for infinity to a setting for about life-size magnification, further improvements of the aberration correction must be sought for.
The arrangement disclosed in the above Japanese Laid-Open Patent Application No. Hei 8-76012 has not realized the capability of focusing up to an object of life-size magnification.